U.S. patent number 10,217,864 [Application Number 15/592,444] was granted by the patent office on 2019-02-26 for double gate vertical finfet semiconductor structure.
This patent grant is currently assigned to GLOBALFOUNDRIES Inc.. The grantee listed for this patent is GLOBALFOUNDRIES Inc.. Invention is credited to Josef Watts, Hui Zang.
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United States Patent |
10,217,864 |
Zang , et al. |
February 26, 2019 |
Double gate vertical FinFET semiconductor structure
Abstract
A semiconductor structure includes a substrate and a vertical
FinFET disposed over the substrate. The vertical FinFET includes: a
bottom source/drain (S/D) region disposed over the substrate, a fin
extending vertically upwards from the bottom S/D region, the fin
having a first (1.sup.st) sidewall, a second (2.sup.nd) sidewall
and a top portion, an upper S/D region disposed over the top
portion of the fin, the fin defining a channel between the bottom
S/D region and the upper S/D region, a 1.sup.st gate structure
having a 1.sup.st metal gate, the 1.sup.st gate structure disposed
on the 1.sup.st sidewall of the fin, and a 2.sup.nd gate structure
having a 2.sup.nd metal gate, the 2.sup.nd gate structure disposed
on the 2.sup.nd sidewall of the fin. The 1.sup.st and 2.sup.nd
metal gates are electrically isolated from each other by the
fin.
Inventors: |
Zang; Hui (Guilderland, NY),
Watts; Josef (Saratoga Springs, NY) |
Applicant: |
Name |
City |
State |
Country |
Type |
GLOBALFOUNDRIES Inc. |
Grand Cayman |
N/A |
KY |
|
|
Assignee: |
GLOBALFOUNDRIES Inc. (Grand
Cayman, KY)
|
Family
ID: |
64098041 |
Appl.
No.: |
15/592,444 |
Filed: |
May 11, 2017 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20180331212 A1 |
Nov 15, 2018 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L
29/4966 (20130101); H01L 29/7831 (20130101); H01L
29/66666 (20130101); H01L 29/7827 (20130101) |
Current International
Class: |
H01L
29/66 (20060101); H01L 29/49 (20060101); H01L
29/78 (20060101) |
Field of
Search: |
;257/329 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Sayadian; Hrayr A
Attorney, Agent or Firm: Thompson Hine LLP Pagette;
Francois
Claims
What is claimed is:
1. A semiconductor structure comprising: a substrate; a vertical
FinFET disposed over the substrate, the vertical FinFET including:
a bottom source/drain (S/D) region disposed over the substrate, a
fin extending vertically upwards from the bottom S/D region, the
fin having a first (1.sup.st) sidewall, a second (2.sup.nd)
sidewall and a top portion, an upper S/D region disposed over the
top portion of the fin, the fin defining a channel between the
bottom S/D region and the upper S/D region, a 1.sup.st gate
structure having a 1.sup.st metal gate, the 1.sup.st gate structure
disposed on the 1.sup.st sidewall of the fin, and a 2.sup.nd gate
structure having a 2.sup.nd metal gate, the 2.sup.nd gate structure
disposed on the 2.sup.nd sidewall of the fin; and wherein the
1.sup.st and 2.sup.nd metal gates are electrically isolated from
each other by the fin.
2. The semiconductor structure of claim 1 comprising: the 1.sup.st
gate structure operable to modulate the conduction of charged
carriers through the channel; the 2.sup.nd gate structure operable
to modulate the conduction of charged carriers through the channel;
and wherein the 1.sup.st and 2.sup.nd gate structures are operable
independently of each other.
3. The semiconductor structure of claim 1 comprising; the fin
extending vertically upwards from the bottom S/D region to the
upper S/D region to define an upper fin height; wherein the upper
fin height is greater than or equal to an upper height of either
the 1.sup.st and 2.sup.nd gate structures.
4. The semiconductor structure of claim 1 comprising: the fin
extending longitudinally along an upper surface of the bottom S/D
region to define a 1.sup.st fin end portion and a 2.sup.nd fin end
portion with a fin intermediate portion extending there between;
wherein the 1.sup.st and 2.sup.nd metal gates are disposed within
the fin intermediate portion of the fin only.
5. The semiconductor structure of claim 1 wherein the upper S/D
region is epitaxially grown.
6. The semiconductor structure of claim 1 comprising: a 1.sup.st CB
contact in electrical contact with the 1.sup.st metal gate, the
1.sup.st CB contact operable to activate the 1.sup.st metal gate;
and a 2.sup.nd CB contact in electrical contact with the 2.sup.nd
metal gate, the 2.sup.nd CB contact operable to activate the
2.sup.nd metal gate; wherein the 1.sup.st and 2.sup.nd CB contacts
are operable to activate their associated 1.sup.st and 2.sup.nd
metal gates independently of each other.
7. The semiconductor structure of claim 1 wherein the 1.sup.st gate
structure comprises: a 1.sup.st lower spacer disposed over the
bottom S/D region, the 1.sup.st metal gate disposed over the
1.sup.st lower spacer, a 1.sup.st upper spacer disposed over the
1.sup.st metal gate, and a 1.sup.st high-k dielectric disposed
between the 1.sup.st metal gate and the fin.
8. The semiconductor structure of claim 1 wherein the 2.sup.nd gate
structure comprises: a 2.sup.nd lower spacer disposed over the
bottom S/D region, the 2.sup.nd metal gate disposed over the
2.sup.nd lower spacer, a 2.sup.nd upper spacer disposed over the
2.sup.nd metal gate, and a 2.sup.nd high-k dielectric disposed
between the 2.sup.nd metal gate and the fin.
9. The semiconductor structure of claim 4 wherein the 1.sup.st and
2.sup.nd fin end portions of the fin have a higher concentration of
one of a p-type dopant and an n-type dopant than the fin
intermediate portion of the fin.
10. The semiconductor structure of claim 4 wherein the 1.sup.st and
2.sup.nd fin end portions of the fin are composed of a dielectric
material.
11. The semiconductor structure of claim 10 wherein the 1.sup.st
and 2.sup.nd fin end portions of the fin are composed of a silicon
dioxide.
Description
TECHNICAL FIELD
The present invention relates to semiconductor devices and methods
of making the same. More specifically, the invention relates to
semiconductor structures having vertical FinFETs, wherein the
FinFETs have two independently controlled gates isolated by a fin
of the vertical FinFETs.
BACKGROUND
Semiconductor structures are constantly being down-sized to meet
increasingly demanding requirements to the speed and functionality
of ultra-high density integrated circuits. As such, Fin Field
Effect Transistors (FinFETs) need to be ever more densely packaged
within the substrate plane defined by the top surface of the
silicone substrate in which the FinFETs are embedded within a
semiconductor structure. However, such down-sizing provides
technical challenges, which are difficult to solve. For example,
leakage currents of FinFETs may increase as the channels within the
FinFETs become smaller in length. Moreover, it is becoming ever
more difficult to increase the overall area (or footprint) along
the substrate plane of a semiconductor structure to accommodate
larger numbers of FinFETs.
In addition to the need to downsize FinFETs in a semiconductor
structure, there is also a growing demand for greater operational
functionality. More specifically, there is a growing demand for
dual speed operation of such FinFETs, wherein a FinFET can operate
at one speed in one mode, and at another faster speed in another
mode.
One class of semiconductor devices that would benefit from such
dual speed FinFET operation would be Static Random Access Memory
(SRAM) cells. SRAM is typically used in personal computers,
workstations, routers, peripheral equipment and the like. SRAM
cells are often composed of various pull-up and pull-down
transistors connected together to form a pair of cross coupled
inverters with opposing logic states. The inverters are connected
to a pair of pass-gate transistors, which control the flow of data
into and out of the SRAM cell during read and write operations.
It is well known that the stability of SRAM cells depends in large
part on the speed of the pass-gate transistors relative to the
speed of the pull-up and pull-down transistors. It is also well
known that for optimum stability, the speed of the pass-gate
transistors should be one speed during a read operation and another
faster speed during a write operation of the SRAM cell. Such dual
speed operating modes can be accomplished with multiple pass-gate
transistors connected in parallel, but would also increase cost,
complexity and size of each SRAM cell.
Accordingly, there is a need for a FinFET that has a smaller
overall footprint for denser packaging. Additionally, there is a
need for such a FinFET to have dual speed operating modes for added
functionality.
BRIEF DESCRIPTION
The present invention offers advantages and alternatives over the
prior art by providing a semiconductor structure having a vertical
FinFET. The vertical FinFET has two independently operated gates
that are separated and electrically isolated from each other by a
fin of the FinFET. The vertical FinFET reduces that overall
footprint along the substrate plane of a semiconductor structure
compared to that of the prior art. Additionally, the independently
operated gates enable at least two speed operation of the
FinFET.
A semiconductor structure in accordance with one or more aspects of
the present invention includes a substrate and a vertical FinFET
disposed over the substrate. The vertical FinFET includes: a bottom
source/drain (S/D) region disposed over the substrate, a fin
extending vertically upwards from the bottom S/D region, the fin
having a first (1.sup.st) sidewall, a second (2.sup.nd) sidewall
and a top portion, an upper S/D region disposed over the top
portion of the fin, the fin defining a channel between the bottom
S/D region and the upper S/D region, a 1.sup.st gate structure
having a 1.sup.st metal gate, the 1.sup.st gate structure disposed
on the 1.sup.st sidewall of the fin, and a 2.sup.nd gate structure
having a 2.sup.nd metal gate, the 2.sup.nd gate structure disposed
on the 2.sup.nd sidewall of the fin.
The 1.sup.st and 2.sup.nd metal gates are electrically isolated
from each other by the fin.
A method in accordance with one or more aspects of the present
invention includes forming a bottom S/D region disposed over a
substrate and a fin extending vertically upwards from a top surface
of the bottom S/D region. A lower spacer layer is disposed over the
bottom S/D region. A high-k dielectric layer is disposed over the
lower spacer layer and the fin. A gate metal layer is disposed over
the high-k dielectric layer. The gate metal layer is etched to
expose 1.sup.st and 2.sup.nd fin end portions of the fin and to
leave the gate metal layer disposed over a fin intermediate portion
of the fin. The gate metal layer is polished to form 1.sup.st and
2.sup.nd metal gates disposed on opposing sidewalls of the fin and
electrically isolated by the fin. The 1.sup.st and 2.sup.nd metal
gates are recessed below a top portion of the fin. A 1.sup.st upper
spacer is disposed over the 1.sup.st metal gate and a 2.sup.nd
upper spacer is disposed over the 2.sup.nd metal gate. An upper S/D
region is epitaxially grown over the top portion of the fin.
DRAWINGS
The invention will be more fully understood from the following
detailed description taken in conjunction with the accompanying
drawings, in which:
FIG. 1A is a perspective view of a prior art exemplary embodiment
of a semiconductor structure having a vertical Fin Field Effect
Transistor (FinFET) disposed over a substrate;
FIG. 1B is a top view of the structure of FIG. 1A;
FIG. 1C is a side view of the structure of FIG. 1B taken along the
line 1C-1C of FIG. 1B;
FIG. 2A is a perspective view of an exemplary embodiment of a
semiconductor structure having a double gate vertical FinFET
disposed over a substrate in accordance with the present
invention;
FIG. 2B is a top view of the structure of FIG. 2A;
FIG. 2C is a side view of the structure of FIG. 2B taken along the
line 2C-2C of FIG. 2B;
FIG. 3 is a perspective view of an exemplary embodiment of the
structure of FIG. 2A at an intermediate stage of its process flow
in accordance with the present invention;
FIG. 4 is a perspective view of an exemplary embodiment of the
structure of FIG. 3 having a bottom source/drain (S/D) region
disposed over a substrate, a fin disposed over the bottom S/D
region and a hardmask layer disposed over the fin in accordance
with the present invention;
FIG. 5 is a perspective view of an exemplary embodiment of the
structure of FIG. 4 having an FOX layer disposed over the substrate
in accordance with the present invention;
FIG. 6 is a perspective view of an exemplary embodiment of the
structure of FIG. 5 having lower spacer layer disposed over the
structure in accordance with the present invention;
FIG. 7 is a perspective view of an exemplary embodiment of the
structure of FIG. 6 having an OPL layer disposed over the structure
in accordance with the present invention;
FIG. 8 is a perspective view of an exemplary embodiment of the
structure of FIG. 7 having the OPL layer removed from the structure
to expose the fin and lower spacer layer in accordance with the
present invention;
FIG. 9 is a perspective view of an exemplary embodiment of the
structure of FIG. 8 having a high-k dielectric layer and gate metal
layer disposed over the structure in accordance with the present
invention;
FIG. 10 is a perspective view of an exemplary embodiment of the
structure of FIG. 9 having a gate mask disposed on the gate metal
layer and having the gate metal layer anisotropically etched in
accordance with the present invention;
FIG. 11 is a perspective view of an exemplary embodiment of the
structure of FIG. 10 having the gate mask removed in accordance
with the present invention;
FIG. 12 is a perspective view of an exemplary embodiment of the
structure of FIG. 11 having another FOX layer disposed over the
structure and the gate metal layer planarized down to the level of
the hardmask layer to form a 1.sup.st and a 2.sup.nd metal gate
separated by the fin in accordance with the present invention;
FIG. 13 is a perspective view of an exemplary embodiment of the
structure of FIG. 12 having the 1.sup.st and 2.sup.nd metal gates
recessed in accordance with the present invention;
FIG. 14 is a perspective view of an exemplary embodiment of the
structure of FIG. 13 having a 1.sup.st and a 2.sup.nd upper spacer
disposed over the 1.sup.st and 2.sup.nd metal gates respectively in
accordance with the present invention;
FIG. 15 is a perspective view of an exemplary embodiment of the
structure of FIG. 14 having the hardmask layer removed to expose a
top portion of the fin in accordance with the present
invention;
FIG. 16 is a perspective view of an exemplary embodiment of the
structure of FIG. 15 having an upper S/D region formed over the top
portion of the fin in accordance with the present invention;
FIG. 17 is a perspective view of another exemplary embodiment of
the structure of FIG. 2A at an intermediate stage of its process
flow, wherein 1.sup.st and 2.sup.nd end portions of the fin are
subjected to an ion implantation process in accordance with the
present invention;
FIG. 18 is a perspective view of another exemplary embodiment of
the structure of FIG. 2A at an intermediate stage of its process
flow, wherein 1.sup.st and 2.sup.nd end portions of the fin are
subjected to a thermal oxidation process in accordance with the
present invention; and
FIG. 19 is a perspective view of the structures of FIG. 17 and FIG.
18 at an end stage of their process flows, wherein the 1.sup.st and
2.sup.nd end portions of the fin are either implanted with a dopant
concentration as a result of the ion implantation process of FIG.
17 or are formed of silicone dioxide as a result of the thermal
oxidation process of FIG. 18 in accordance with the present
invention.
DETAILED DESCRIPTION
Certain exemplary embodiments will now be described to provide an
overall understanding of the principles of the structure, function,
manufacture, and use of the methods, systems, and devices disclosed
herein. One or more examples of these embodiments are illustrated
in the accompanying drawings. Those skilled in the art will
understand that the methods, systems, and devices specifically
described herein and illustrated in the accompanying drawings are
non-limiting exemplary embodiments and that the scope of the
present invention is defined solely by the claims. The features
illustrated or described in connection with one exemplary
embodiment may be combined with the features of other embodiments.
Such modifications and variations are intended to be included
within the scope of the present invention.
FIGS. 1A-1C illustrate an exemplary embodiment of a prior art
vertical FinFET. FIGS. 2A-2C illustrate an exemplary embodiment of
a double gate vertical FinFET in accordance with the present
invention. FIGS. 3-18 illustrate a method of making the double gate
vertical FinFET in accordance with the present invention.
Referring to FIGS. 1A, 1B and 1C, wherein: FIG. 1A is a perspective
view of a prior art exemplary embodiment of a semiconductor
structure 10 having a vertical Fin Field Effect Transistor (FinFET)
12 disposed over a substrate 14; FIG. 1B is a top view of the
structure 10; and FIG. 1C is a cross-sectional view of the
structure 10 taken along the line 1C-1C of FIG. 1B.
Semiconductor structure 10 includes a FinFET 12 disposed over the
bulk substrate 14. A flowable oxide (FOX) layer 16 is disposed over
a top surface 18 of the bulk substrate 14. The FOX layer 16
surrounds a bottom source/drain (S/D) region 20 of the FinFET 12,
which extends vertically upwards and longitudinally across the top
surface 18 of the substrate 14. In addition to the bottom S/D
region 20, the FinFET 12 includes a fin 22 extending vertically
upwards and longitudinally across the bottom S/D region 20. An
upper S/D region 24 disposed over a top end portion of the fin 22.
The FinFET 12 also includes a single gate structure 26, which
completely surrounds the perimeter of fin 22.
For purposes herein, the top surface 18 of the bulk substrate 14
defines a substrate plane, wherein the longitudinal direction of
the fin 22 disposed over the top surface 18 will be considered the
X direction of the substrate plane and the direction perpendicular
to the X direction will be considered the Y direction of the
substrate plane. Additionally, the direction perpendicular to the
substrate plane will be considered the vertical, or Z
direction.
The gate structure 26 includes a lower gate spacer 28, an upper
gate spacer 30, a high-k dielectric 32 and a metal gate 34. The
lower and upper gate spacers 28, 30 may be composed of a dielectric
material such as SiN, SiNC, SiBCN or similar. The high-k dielectric
may be composed of such material as hafnium dioxide (HfO2), nitride
hafnium silicates (HfSiON) or the like. The metal gate can be a
metal stack of a work-function metal (which can be TiN, TaN, TiCAl,
other metal-nitrides or similar materials) and a gate electrode
metal (which may be Al, W, Cu or similar metal). The lower and
upper gate spacers 28, 30 are used to insulate the metal gate 34
from the bottom and upper S/D regions 20, 24 respectively. The gate
dielectric is used to electrically insulate the metal gate 34 from
the fin 22. The work-function metal of the metal gate 34 provides
the work-function needed for proper FinFET operation, but typically
has 10 to 100 times larger resistivity than the gate electrode
metal. The gate electrode metal of the metal gate 34 typically has
a very low resistivity.
Because the single gate structure 26 completely surrounds the fin
22, the singe gate structure 26 is disposed against both opposing
sidewalls 36 and 38 of fin 22. As such, there is electrical
conductivity between the regions of the metal gate 34 that are
disposed on the opposing sidewalls 36 and 38. Therefore, only one
CB (gate) contact 40 is needed to operate the entire gate
structure. Additionally, however, there is only one mode of
operation of the FinFET 12. That is, the FinFET 12 has only one
operating speed and current that can be induced by the single gate
structure 26.
Extending upwards in the vertical direction from the bottom S/D
region 20 is a 1.sup.st trench silicide (TS) contact 42. Extending
upwards in the vertical direction from the upper S/D region 24 is a
2.sup.nd TS contact 44. The TS contacts 42, 44 provide electrical
conductivity between the S/D regions 20, 24 and active interconnect
lines (not shown) used to operate the FinFET 12.
Referring to FIGS. 2A, 2B, and 2C, wherein: FIG. 2A is a
perspective view of an exemplary embodiment of a semiconductor
structure 100 having a double gate vertical FinFET 102 disposed
over a substrate 104 in accordance with the present invention; FIG.
2B is a top view of the structure 100; and FIG. 2C is a side view
of the structure 100 taken along the line 2C-2C of FIG. 2B.
Semiconductor structure 100 includes a double gate vertical FinFET
102 disposed over a substrate 104. A flowable oxide (FOX) layer 106
is disposed over a top surface 108 of the bulk substrate 104. The
FOX layer 106 surrounds a bottom source/drain (S/D) region 110 of
the FinFET 102.
In addition to the bottom S/D region 110, the FinFET 102 includes a
fin 112 extending vertically upwards from the bottom S/D region
110. The fin 112 has a first (1.sup.st) sidewall 114, a second
(2.sup.nd) sidewall 116 and a top portion 118. An upper S/D region
120 of FinFET 102 is disposed over the top portion 118 of the fin
112. The upper S/D region may be epitaxially grown. The fin defines
a channel 122 between the bottom S/D region 110 and the upper S/D
region 120.
The FinFET 102 also includes a 1.sup.st gate structure 124 having a
1.sup.st metal gate 126, wherein the 1.sup.st gate structure 124 is
disposed on the 1.sup.st sidewall 114 of the fin 112. The FinFET
102 also includes a 2.sup.nd gate structure 128 having a 2.sup.nd
metal gate 130, wherein the 2.sup.nd gate structure 128 is disposed
on the 2.sup.nd sidewall 116 of the fin 112.
The 1.sup.st and 2.sup.nd metal gates 126, 130 are electrically
isolated from each other by the fin 112. More specifically, there
is no electrically conductive path between the 1.sup.st and
2.sup.nd metal gates 126, 130 that is not interrupted by a
dielectric layer. As such, the 1.sup.st gate structure 124 is
operable to modulate the conduction of charged carriers through the
channel 122. Additionally the 2.sup.nd gate structure 128 is also
operable to modulate the conduction of charged carriers through the
channel 122. Moreover, the 1.sup.st and 2.sup.nd gate structures
124, 128 are operable independently of each other and the channel
conduction is determined by the potential on both gates.
The fin 112 extends vertically upwards from the bottom S/D region
110 to the upper S/D region 120 to define a fin height 132. In
order to isolate the 1.sup.st and 2.sup.nd metal gates 126, 130,
the fin height 132 is greater than or equal to a height 134 of the
1.sup.st structure 124 and greater than or equal to a height 136 of
the 2.sup.nd gate structure 128.
The fin 112 also extends longitudinally along an upper surface of
the bottom S/D region 110 to define a 1.sup.st fin end portion 138
and a 2.sup.nd fin end portion 140 with a fin intermediate portion
142 extending therebetween (best seen in FIG. 2A). The 1.sup.st and
2.sup.nd metal gates 126, 130, are disposed within the fin
intermediate portion 142 of the fin 112 only, in order to isolate
the 1.sup.st and 2.sup.nd metal gates 126, 130 from each other.
That is, no portion of the 1.sup.st and 2.sup.nd metal gates 126,
130 (and in this embodiment, no portion of the 1.sup.st and
2.sup.nd metal gate structures 124, 128) are disposed against the
1.sup.st and 2.sup.nd fin end portions 138, 140.
For purposes herein, the top surface 108 of the substrate 104
defines a substrate plane, wherein the longitudinal direction of
the fin 112 disposed over the top surface 108 will be considered
the X direction of the substrate plane and the direction
perpendicular to the X direction will be considered the Y direction
of the substrate plane. Additionally, the direction perpendicular
to the substrate plane will be considered the vertical, or Z
direction.
In addition to the 1.sup.st metal gate 126, the 1.sup.st gate
structure 124 also includes a 1.sup.st lower spacer 144, a 1.sup.st
upper spacer 146 and a 1.sup.st high-k dielectric 148. The 1.sup.st
lower spacer 144 is disposed over the bottom S/D region 110. The
1.sup.st metal gate 126 is disposed over the 1.sup.st lower spacer
144. The 1.sup.st upper spacer 146 is disposed over the 1.sup.st
metal gate 126. The 1.sup.st high-k dielectric 148 is disposed
between the 1.sup.st metal gate 126 and the fin 112. Additionally,
in this embodiment, the 1.sup.st high-k dielectric 148 is disposed
between the 1.sup.st metal gate 126 and the 1.sup.st lower spacer
144.
In addition to the 2.sup.nd metal gate 130, the 2.sup.nd gate
structure 128 also includes a 2.sup.nd lower spacer 150, a 2.sup.nd
upper spacer 152 and a 2.sup.nd high-k dielectric 154. The 2.sup.nd
lower spacer 150 is disposed over the bottom S/D region 110. The
2.sup.nd metal gate 130 is disposed over the 2.sup.nd lower spacer
150. The 2.sup.nd upper spacer 152 is disposed over the 2.sup.nd
metal gate 130. The 2.sup.nd high-k dielectric 154 is disposed
between the 2.sup.nd metal gate 130 and the fin 112. Additionally,
in this embodiment, the 2.sup.nd high-k dielectric 154 is disposed
between the 2.sup.nd metal gate 130 and the 2.sup.nd lower spacer
150.
The 1.sup.st and 2.sup.nd lower gate spacers 144, 150, as well as
the 1.sup.st and 2.sup.nd upper gate spacers 146, 152 may be
composed of a dielectric material such as SiN, SiNC, SiBCN or
similar. The 1.sup.st and 2.sup.nd high-k dielectrics 148, 154 may
be composed of such material as hafnium dioxide (HfO2), nitride
hafnium silicates (HfSiON) or the like. The 1.sup.st and 2.sup.nd
metal gates 126, 130 can be a metal stack of a work-function metal
(which can be TiN, TaN, TiCAl, other metal-nitrides or similar
materials) and a gate electrode metal (which may be Al, W, Cu or
similar metal). The lower and upper gate spacers 144, 146, 150, 152
are used to insulate the metal gates 126, 130 from the bottom and
upper S/D regions 110, 120 respectively. The 1.sup.st and 2.sup.nd
high-k dielectrics 148, 154 are used to electrically insulate the
metal gates 126, 130 from the fin 112. The work-function metal of
the metal gates 126, 130 provides the work-function needed for
proper FinFET operation, but typically has 10 to 100 times larger
resistivity than the gate electrode metal. The gate electrode metal
of the metal gates 126, 130 typically has a very low resistivity.
In this exemplary embodiment, the fin 112 electrically isolates the
1.sup.st and 2.sup.nd gate structures 124, 128.
The semiconductor structure 100 also includes a 1.sup.st CB contact
156 in electrical contact with the 1.sup.st metal gate 126, wherein
the 1.sup.st CB contact 156 is operable to activate the 1.sup.st
metal gate 126. Additionally, structure 100 includes a 2.sup.nd CB
contact 158 in electrical contact with the 2.sup.nd metal gate 130,
wherein the 2.sup.nd CB contact 158 is operable to activate the
2.sup.nd metal gate 130. Moreover, the 1.sup.st and 2.sup.nd CB
contacts 156, 158 are operable to activate their associated
1.sup.st and 2.sup.nd metal gates 126, 130 independently of each
other.
The 1.sup.st and 2.sup.nd CB contacts 156, 158 may be composed of
the same or similar materials as that of the gate electrode metal
of the 1.sup.st and 2.sup.nd metal gates 126, 130. Therefore, the
1.sup.st and 2.sup.nd CB contacts 156, 158 may be composed of Al,
W, Cu or similar metals.
Extending upwards in the vertical direction from the bottom S/D
region 110 is a 1.sup.st trench silicide (TS) contact 160.
Extending upwards in the vertical direction from the upper S/D
region 120 is a 2.sup.nd TS contact 162. The TS contacts 160, 162
provide electrical conductivity between the S/D regions 110, 120
and active interconnect lines (not shown) used to operate the
FinFET 102.
Referring to FIGS. 3-18, an exemplary embodiment of a method of
making the semiconductor structure 100 having the double gate
vertical FinFET 102 in accordance with the present invention is
illustrated.
Referring more specifically to FIG. 3, a hardmask layer 200 is
first disposed over the substrate 104 of structure 100. The
hardmask layer 200 may be composed of such material as silicon
nitride (SNi) or similar. The hardmask layer 200 may be disposed by
physical vapor deposition (PVD), chemical vapor deposition (CVD) or
the like.
The hardmask layer 200 is then patterned and etched to form the fin
112 in the substrate 104. A portion of the hardmask layer 200
remains disposed over the top portion 118 of the fin 112 after the
etching process.
Referring to FIG. 4, a portion of the substrate 104, which
surrounds the fin 112, is then patterned and etched to form the
bottom S/D region 110 into the structure 100. The result at this
stage of the process flow is that the bottom S/D region 110 is
formed disposed over the substrate 104 and extending upwards (in
the Z direction) from the top surface 108 of the bottom S/D region
110. Additionally, the fin 112 is formed extending upwards from a
top surface 202 of the bottom S/D region 110. The fin 112 is also
formed extending longitudinally across the S/D region 110.
Referring to FIG. 5, the flowable oxide layer (FOX) layer 106 is
next disposed over the structure 100 such that the top surface 202
of the bottom S/D region 110 is not covered by the FOX layer 106.
The FOX layer 106 may be disposed through CVD, PVD or other similar
process.
Referring to FIG. 6, next a lower spacer layer 204 is disposed over
the FOX layer 106, the top surface 202 of the bottom S/D region 110
and the fin 112. This may be done by a CVD, PVD, atomic layer
deposition (ALD) or similar process.
The lower spacer layer 204 is composed of the same material as the
1.sup.st and 2.sup.nd lower spacers 144, 150. Accordingly, the
lower spacer layer 204 may be composed of SiN, SiNC, SiBCN or
similar.
Referring to FIG. 7, at this stage of the process flow, the lower
spacer layer 204 coats both sidewalls 114, 116 of the fin 112 and
must be removed from those sidewalls. In order to accomplish this
an organic planarization layer (OPL) 205 may be disposed over the
entire structure 100 to completely cover the fin 112. The OPL (or
OPL layer) 205 may be deposited using a spin-on deposition process.
The OPL 205 may be composed of an organic material such as an
amorphous carbon or other similar material.
Referring to FIG. 8, next the OPL 205 is etched away, along with
the portion of the lower spacer layer 204 that is disposed on the
fin 112. Accordingly, the fin 112 and a portion of the lower spacer
layer 204 that is disposed over the FOX layer 106 are left
exposed.
Referring to FIG. 9, next in the process flow a high-k dielectric
layer 206 is disposed over the lower spacer layer 204 and the fin
112. This may be done by an ALD process or similar.
The high-k dielectric layer 206 is composed of the same material as
the 1.sup.st and 2.sup.nd high-k dielectrics 148, 154. Accordingly,
the high-k dielectric layer 206 may be composed of such material as
hafnium dioxide (HfO2), nitride hafnium silicates (HfSiON) or the
like.
Next a gate metal layer 208 is disposed over the high-k dielectric
layer 206. This may be done by CVD, PVD, electroplating or other
similar process.
The gate metal layer 208 is composed of the same materials as the
1.sup.st and 2.sup.nd metal gates 126, 130. As such, the gate metal
layer 208 may be a metal stack of a work-function metal (which can
be TiN, TaN, TiCAl, other metal-nitrides or similar materials) and
a gate electrode metal (which may be Al, W, Cu or similar
metal).
Referring to FIG. 10, next a lithographic stack 210 is disposed
over the structure 100. The lithographic stack 210 can be composed
of several different kinds of layers, depending on such parameters
as the application requirements, design or proprietary preferences
or the like. One such stack of layers includes a stack of four thin
films which includes (from top to bottom) a resist layer, a bottom
antireflective coating (BARC) layer, a SiON dielectric layer 128
and a spin-on hardmask (SOH) layer.
The lithographic stack 210 is next patterned, through well-known
lithographic techniques, to form a gate mask 212 over the fin
intermediate portion 142 of the fin 112 and not over the 1.sup.st
and 2.sup.nd fin end portions 138, 140 of the fin 112. Next any
portions of the gate metal layer 208 not covered by the gate mask
212 are etched to expose the 1.sup.st and 2.sup.nd fin end portions
138, 140 of the fin 112 and to leave the gate metal layer 208
disposed over the fin intermediate portion 142 of the fin 112.
Referring to FIG. 11, next the gate mask 212 is removed. This may
be done by a wet etch process or similar.
Referring to FIG. 12, next another FOX layer 214 is disposed over
the structure 100 to cover the gate metal layer 208 and the lower
spacer layer 204. The FOX layer 214, the gate metal layer 208 and
the high-k dielectric layer 206 are then polished down to the level
of the hardmask layer 200, which is disposed over the top portion
of the fin.
At this stage of the process flow, the gate metal layer has been
separated by the fin 112 to form the 1.sup.st and 2.sup.nd metal
gates 114, 116, which are now disposed on opposing sidewalls 114,
116 of the fin 112. The 1.sup.st and 2.sup.nd metal gates 114, 116
are disposed only on the fin intermediate portion 142 of the fin
112, and not on the 1.sup.st end portion 138 or the 2.sup.nd end
portion 140 of the fin 112. As such, the 1.sup.st and 2.sup.nd
metal gates 114, 116 are now electrically isolated by the fin
112.
Additionally, the high-k dielectric layer 206 has been separated by
the fin 112 to form the 1.sup.st high-k dielectric 148 and the
2.sup.nd high-k dielectric 154. The 1.sup.st and 2.sup.nd high-k
dielectrics are now disposed between the 1.sup.st and 2.sup.nd
metal gates 114, 116 and the fin 112 (best seen in FIG. 2C).
Referring to FIG. 13, the 1.sup.st and 2.sup.nd metal gates 126,
130 are next recessed below the hardmask layer 200 and below a top
portion of the fin 112. This can be done by a reactive ion etch
(RIE) process or similar.
Referring to FIG. 14, next the 1.sup.st upper spacer 146 is
disposed over the 1.sup.st metal gate 126 and the 2.sup.nd upper
spacer 152 is disposed over the 2.sup.nd metal gate 130. This can
be accomplished by first disposing an upper spacer layer (not
shown) over the entire structure 100. The upper spacer layer can
then be polished down to the level of the hardmask 200 to form the
1.sup.st and 2.sup.nd upper spacers 146, 152 disposed over their
associated 1.sup.st and 2.sup.nd metal gates 126, 130. Thereafter,
the 1.sup.st and 2.sup.nd upper spacers 146, 152 can be recessed
down (by a RIE process or similar) to a desired level below the top
portion of the fin 112.
Referring to FIG. 15, next the hardmask layer 200 is removed from
the top portion 118 of the fin 112, to expose the top portion of
the fin 118. This can be done by a wet etch process or similar.
Referring to FIG. 16, next the upper S/D region 120 is formed over
the top portion 118 of the fin 112. This can be accomplished by a
process of epitaxially growing the upper S/D region 120 over the
top portion 118 of the fin 112 or other similar process.
Once the upper S/D region 120 is formed, the FOX layer 214 can be
removed to provide the structure 100 shown in FIGS. 2A, 2B and 2C
without the 1.sup.st CB contact 156, the 2.sup.nd CB contact 158,
the 1.sup.st TS contact 160 or the 2.sup.nd TS contact 162.
However, those CB contacts 156, 158 and TS contacts 160, 162 may be
added later in the process flow by well-known methods.
The dual gate vertical FinFET 102 of structure 100 (best seen in
FIGS. 2A, 2B and 2C) advantageously has at least two operating
speeds by virtue of its two independent gate structures 124, 128.
Additionally, the vertical FinFET 102 has a smaller footprint along
the X and Y directions (i.e., the substrate plane) than
non-vertical FinFETs.
Referring to FIG. 17, because the gate structures 124 and 128 do
not cover the 1.sup.st and 2.sup.nd end portions 138, 140 of fin
112, those end portions 138, 140 may have a disproportionally
larger leakage current then the fin intermediate portion 142 of the
fin 112. To help prevent such a disproportionally large leakage
current, the 1.sup.st and 2.sup.nd end portions 138, 140 may be
subjected to an implantation process 216 earlier in the process
flow to change the concentration of dopant level of the 1.sup.st
and 2.sup.nd end portions 138, 140 relative to the concentration of
dopant levels of the fin intermediate portion 142.
By way of example, FIG. 17 shows the structure 100 at a stage
equivalent to that of FIG. 10, wherein the gate mask 212 is still
disposed over the structure 100. At this stage, only the 1.sup.st
and 2.sup.nd end portions 138, 140 are exposed and the fin
intermediate portion 142 is protected by the gate metal layer 208.
The ion implantation process 216 can then be carried out on the
1.sup.st and 2.sup.nd end portions 138, 140 leaving the fin
intermediate portion 142 largely unaffected.
If the fin intermediate portion 142 is doped primarily with a
concentration of n-type dopants, then the 1.sup.st and 2.sup.nd end
portions can be doped with a higher concentration of n-type dopants
during the ion implantation process 216. If the fin intermediate
portion 142 is doped primarily with a concentration of p-type
dopants, than the 1.sup.st and 2.sup.nd end portions can be doped
with a higher concentration of p-type dopants during the ion
implantation process 216.
In other words, one of an n-type dopant and a p-type dopant may be
implanted during the ion implantation process 216 in the 1.sup.st
and 2.sup.nd fin end portions 138, 140 of the fin 112, such that
the 1.sup.st and 2.sup.nd fin end portions 138, 140 have a higher
concentration of the one of the n-type dopant and the p-type dopant
than the fin intermediate portion 142 of the fin 140. The result is
that the 1.sup.st and 2.sup.nd fin end portions 138, 140 of the fin
112 will have a higher concentration of one of a p-type dopant and
an n-type dopant than the fin intermediate portion 142 of the fin
112.
Referring to FIG. 18, an alternative method of helping to prevent
such disproportionately larger leakage current would be to form the
1.sup.st and 2.sup.nd fin end portions 138, 140 such that the
1.sup.st and 2.sup.nd fin end portions 138, 140 of the fin 112 are
composed of a dielectric material. One such way of accomplishing
this would be to subject the 1.sup.st and 2.sup.nd end portions
138, 140 to a thermal oxidation process 218 earlier in the process
flow.
By way of example, FIG. 18 shows the structure 100 at a stage
equivalent to that of FIG. 10, wherein the gate mask 212 is still
disposed over the structure 100. At this stage, only the 1.sup.st
and 2.sup.nd end portions 138, 140 are exposed and the fin
intermediate portion 142 is protected by the gate metal layer 208.
The thermal oxidation process 218 can then be carried out on the
1.sup.st and 2.sup.nd end portions 138, 140 leaving the fin
intermediate portion 142 largely unaffected.
The 1.sup.st and 2.sup.nd fin end portions 138, 140 of the fin 112
may be thermally oxidized such that the 1.sup.st and 2.sup.nd fin
end portions 138, 140 of the fin 112 become composed primarily of a
silicon dioxide. Since the silicon dioxide is a dielectric
material, the leakage current though the 1.sup.st and 2.sup.nd end
portions 138, 140 will be reduced.
Referring to FIG. 19, the resulting structure 100 with the dual
gate vertical FinFET 102 after either the ion implantation process
216 or thermal oxidation process 218 is illustrated. The fin 112
may have 1.sup.st and 2.sup.nd fin end portions 138, 140 that have
a higher concentration of an n-type or a p-type dopant than the fin
intermediate portion 142 due to the ion implantation process 216.
Alternatively, the fin 112 may have 1.sup.st and 2.sup.nd fin end
portions 138, 140 that are composed of a dielectric material such
as silicone dioxide due to the thermal oxidation process 218. In
either case the leakage current of the end portions 138, 140 will
be reduced.
The FinFET 102 will also advantageously have at least a dual mode
of operation wherein in one mode, the current and operating speed
will be larger and faster than in the other mode. This is due to
the independent operation of the two gate structures 124, 128 that
are electrically isolated by the fin 112.
Additionally, the footprint of the vertical FinFET 102 in the X
direction and Y direction (the substrate plane) will be smaller
than non-vertical FinFETs. This is because the bottom S/D region
110, the fin 112 and the upper S/D region 120 are stacked
vertically (in the Z direction) on top of each other
respectively.
Although the invention has been described by reference to specific
embodiments, it should be understood that numerous changes may be
made within the spirit and scope of the inventive concepts
described. Accordingly, it is intended that the invention not be
limited to the described embodiments, but that it have the full
scope defined by the language of the following claims.
* * * * *